It’s worth noting that a couple of other venture-backed Internet companies have hired banks to help them sell themselves — at least according to our sources — including social news site Digg and social network Bebo.

Plaxo declined comment.

The company has released a stream of new products built around the concept of a “social graph” — the connections you make with others on social networks, through your email, IM and phone, and other forms of digital communication.

The Mountain View, Calif.-based company launched a service called “Pulse,” in August, that displays your friends’ latest activities on sites like Twitter, YouTube and Flickr within a cascading stream on its own site (our coverage).

More recently, it introduced a way to see Pulse through Microsoft’s popular email program Outlook (our coverage), via a plug-in. The idea was based, as far as we can tell, on Facebook’s “news feed,” which shows you the latest activities of your Facebook friends. Plaxo claims Pulse has one million unique monthly visitors, a significant increase from the 250,000 it had at the beginning over November.

I find the service most useful for occasionally syncing the address books on Gmail, my Mac, and on other sites.

Who would want to buy Plaxo? Some of the more obvious potential purchasers — Microsoft, Yahoo, Google, etc. — already have access to millions of users’ address books. Google, at least, is working on its own sort of “social graph” aggregator. That company is rumored to be working on a similar sort of activity stream for Gmail, that lets you see what your Gmail contacts are up to on other Google products. Other tech companies may want the contact information data and services that Plaxo has — maybe Cisco, one of the company’s investors, that has recently been buying web companies (our coverage)?

Plaxo claims to have 20 million total users for its addressing syncing service, with another 15 million additional accounts hosted on other sites through partnerships.